The technical scope of the invention is that of bumpers for vehicles, and notably for motor vehicles.
Existing bumpers do not allow impacts to be absorbed that occur when the vehicle is at a speed greater than 15 km/h without damage to the body.
So as to restrict the violence of frontal impacts it is known to design bumpers fitted with shock-absorbing means.
Thus, patents U.S. Pat. Nos. 3,822,076 and 3,708,194 show vehicles fitted with an inflatable bag that is deployed to the front of the bumper in the event of sudden deceleration. This bag allows part of the kinetic energy to be absorbed and protects the vehicle""s occupants.
Said devices employing deployable bags are complicated to implement. To protect the vehicle, the bag must have a substantial volume when inflated and is thus not able to deploy both rapidly and reliably. Additionally, the folded bag must only occupy a small amount of space, its casing is therefore thin and not very strong. It will burst upon impacting an obstacle and will therefore afford little protection.
Another problem with known systems lies in that they only provide a single level of shock-absorption for the bumper. Said bumper is therefore not able to be suitably adapted to various situations whether related to the intensity of impact or its position with respect to the median axis of the vehicle.
An impact located on one of the sides of the bumper can thus be noted to cause the vehicle to wrap itself around the obstacle thereby seriously prejudicing the safety of the vehicle""s occupants.
Patent U.S. Pat. No. 5,651,569 describes another device in which the bumper incorporates a reinforced rubber bag that is permanently inflated by means of a compressible fluid and that is encased in a metal shell.
The bag is inflated when the bumper is mounted onto the vehicle and it allows the impacts received by the bumper to be distributed and absorbed by the compression of said fluid.
However, such a device suffers nevertheless from certain drawbacks.
Thus, the bag is likely to gradually deflate over time, thereby reducing its shock-absorbing capabilities.
Additionally, such a system provides a single level of shock-absorption for the bumper. It is therefore not able to be suitably adapted to various situations whether related to the intensity of impact or its position with respect to the median axis of the vehicle.
Patents DE19514191 and EP850807 describe bumpers that are attached to the vehicle by means of pyrotechnically controlled actuators. Such systems are also unable to be suitably adapted to various situations whether related to the intensity of impact or its position with respect to the median axis of the vehicle.
Thus, the bumper proposed by the invention provides greater shock-absorbing capabilities that can be modulated according to the force and/or position of the impact received.
The invention thus relates to a bumper for a vehicle fitted with shock-absorbing means, and comprising a rigid support linked to the vehicle onto which a shell intended to receive the impacts is fitted, said shock-absorbing means comprising at least two pyrotechnic actuators linking the rigid support to the vehicle, said actuators being activated by a control system linked to at least one impact and/or deceleration sensor, said bumper being characterised in that each pyrotechnic actuator incorporates at least two gas-generating powder tablets able to be primed individually by the control system so as to provide the actuator with at least two efforts of different intensities.
The control system will be advantageously linked to means allowing the position of the impact received by the vehicle to be located with respect to the median axis of the vehicle, and the control system will then initiate the nearest actuator to the point of impact with a greater effort than that transmitted to the actuator furthest away.
The impact-locating means will be advantageously constituted by the spacing of at least two impact sensors on either side of the median axis of the vehicle.
According to a first embodiment of the invention, the bumper incorporates at least one block of shock-absorbing material placed between the rigid support and the shell.
Each shock-absorbing block can be formed of hollow balls arranged in a matrix of plastic material, said balls being crushed under impact to the shell.
According to a second embodiment of the invention, the shock-absorbing means comprise at least one inner volume in the shell that can be pressurised by means of a compressible fluid supplied by at least one generator initiated by the control system linked to at least one impact and/or deceleration sensor.
Advantageously, the pressurizable volume can comprise at least one casing made of an elastic material such as rubber, reinforced or not, the casing being arranged between the rigid support and the shell.
The casing can incorporate longitudinal and/or transversal partitions delimiting at least two inner cavities in the casing.
The fluid generator or generators intended to inflate the casing or casings will preferably be pyrotechnic gas generators.
According to another embodiment, the device can incorporate two gas generators.
In this case, the control system will initiate one or other gas generator according to a different level of impact or deceleration.